1. Field of the Invention
The present invention relates to an apparatus, a method, and a computer-readable recording medium for distributing position data.
2. Description of the Related Art
Conventionally, the position of a communication terminal of a user is identified by using a GPS (Global Positioning System). With the GPS, wireless signals indicating time are transmitted from approximately 30 GPS satellites orbiting the earth. Then, a communication terminal located on earth uses its receiver to receive the wireless signals and calculates the difference between the time in which the wireless signals are transmitted from the GPS satellites and the time in which the wireless signals from the GPS satellites are received by the receiver of the communication terminal. The communication terminal performs the calculation with respect to at least 4 GPS satellites and identifies its position on earth based on the result of the calculation.
In recent years, size and power consumption of the receiver used for GPS communication are becoming smaller. For example, a GPS receiver is installed in a small battery-powered communication terminal such as a mobile phone.
However, with the GPS, it is difficult for the wireless signals of the GPS to reach a communication terminal located indoors. Therefore, another system is desired for indoor positioning. One example of such system is IMES (Indoor MEssaging System).
A distribution apparatus, which distributes wireless signals by using IMES, can distribute the wireless signals with the same electric waveform as the electric waveform of the wireless signals transmitted by GPS satellites. Therefore, the communication terminals that receive the wireless signals can use the same reception hardware (hardware used for reception) as the reception hardware used for GPS communication. Further, reception software (software used for reception) used for GPS communication can also be used by slightly modifying the reception software. Because position data indicating the position of the IMES distribution apparatus is distributed instead of distributing time data (data indicating time), the communication terminal that receives the wireless signals simply needs to receive the position data and does not need to calculate time difference unlike outdoor positioning.
For example, Japanese Laid-Open Patent Publication No. 2012-145457 discloses a method dedicated to measuring the walking movement of a person. That is, the disclosed method measures the position/direction of a pedestrian by using a sensor(s) (e.g., acceleration sensor, gyro sensor, magnetometric sensor, temperature sensor, barometric pressure sensor) installed in a communication terminal. This method is also referred to as a PDR (Pedestrian Dead Reckoning) method.
By combining an autonomous position measuring method using IMES and a relative position measuring method using PDR, a communication terminal installed with an IMES receiver can obtain current position data at any place of an indoor area. In a case where there is a significant error in the relative position data obtained by the relative position measuring method, it may become necessary to correct the current position data by referring to absolute position data obtained by the method using IMES. However, because position measurement signals of the IMES are transmitted throughout a predetermined range, the position data obtained from the IMES may also have a significant error depending on the position of the communication terminal receiving the position measurement signal.